Native Decky UI and difficulty filters

Replaces the custom-styled browser with native Decky tabs, song rows, dropdowns, and a filter dialog, following Animation Changer and CSS Loader patterns.

• Adds Top This Year and Top All Time collections. Year/week/month refer to chart upload windows, ranked by total downloads.
• Adds Easy, Normal, Hard, Extreme, and XD filtering with inclusive minimum/maximum rating sliders.
• Adds easiest/hardest, download-count, and alphabetical sorting across the full matching result before pagination.
• Fixes skipped feed pages and truncated broad searches. Requests narrower results from SpinShare and caches searches for five minutes.
• Preserves the HTTPS certificate fix and existing download/delete safeguards.

Validation: 36 backend tests, TypeScript checks, frontend build, ZIP integrity, and live ranking/filter/pagination checks. Native rendering and gamepad behavior still require verification on a Steam Deck. Initial broad year/all-time requests can take a minute or two.

Install the attached spinshare-decky-0.2.0.zip through Decky. The automatically generated source archives are not installable plugins.

Fix SteamOS HTTPS certificate verification

Load the system certificate bundle for catalogue requests and song downloads while retaining certificate and hostname verification. Verified with 16 tests, a frontend build, and a live catalogue request with an empty Python default trust store. Install the attached plugin ZIP through Decky; the automatic source-code archives are not installable plugins. Device confirmation remains pending.